Stem cells refer to cells which are in a pre-differentiation stage prior to the stage of differentiating into cells forming respective tissues, and refer to cells which are in an undifferentiated state where they exhibit the ability of self-renewal by which the cells may proliferate infinitely and pluripotency which is potential by which the cells may differentiate into a diverse range of cell types of tissues by specific differentiation stimulation. That is, it is required for the stem cells that the ability of self-renewal of the cell is maintained without decreasing even when the cells are continuously cultured, and the cells may differentiate into various types of cells. The stem cells include embryonic stem cells, adult stem cells, induced pluripotent stem cells (iPS cells), etc.
Among them, the induced pluripotent stem cells denote cells restored to be in the pluripotent cell stage which is the early stage of cell production like embryonic stem cells by restoring completely differentiated somatic cells to be in an undifferentiated cell stage. When the induced pluripotent stem cells are induced to differentiate using somatic cells isolated from one's own body, there is no problem of transplant rejection, and since any egg or embryo is used for preparing the induced pluripotent stem cells, ethical issues are addressed. In this respect, many scientists have expected the induced pluripotent stem cells to fundamentally resolve the treatment of various diseases and organ damage.
In this point of view, a lot of methods of differentiation of the induced pluripotent stem cells into many cells and many techniques for treating diseases using the above-described methods have been developed, and Korean Unexamined Patent Application Publication No. 2014-0125682 disclosed “Pharmaceutical Composition for the Treatment of Stroke Comprising Neural Precursor Cells Derived from Human Induced Pluripotent Stem Cells”.
However, the stem cells are undifferentiated cells, it is difficult to predict which type of cells into which the stem cells later differentiate, and there may be a problem of mutations or genetic abnormalities. Accordingly, when the stem cells are to be used, there is a need for techniques by which the stem cell may be induced to differentiate into a specific type of cell.
Meanwhile, a cornea is the transparent layer of the eye surface positioned at the center portion of the eye, which is an organ protecting the eye from the outside. The external side of the cornea is an epithelial layer, which is a protecting layer of a tissue which is regenerated despite being damaged. However, Bowman's membrane and corneal endothelial which are located at a more inner side than an epithelial layer are not regenerated once damaged.
Consequently, the inner side of the epithelial layer in the cornea of the eye is not regenerated once damaged, and thus vision may be severely impaired or lost. Accordingly, there is a need to perform a surgical treatment for the cornea or replace the cornea through corneal transplantation, etc.
However, regarding corneal transplantation, infants are difficult to remain stable after corneal transplantation, various complications may develop, there may be the problem of immunological rejection because a donor cornea is transplanted, and when patients with corneal dystrophy have corneal transplants, corneal dystrophy is likely to recur. Moreover, there is a severe lack of donated corneas to perform corneal transplant.
With such a background, the inventors of the present invention determined a method of inducing differentiation of a stem cell into a corneal limbal stem cell which is necessary for cornea regeneration, thereby completing the present invention.